I like singing free karaoke app too, and I am using at the moment the Star maker app. Though you need to upgrade if you want to become VIP, however it is not necessary since they have different competitions where you can join and if you win you win a short VIP access. I am in free app and I can still sing different songs. I have tries Smule app too but I most prefer Star maker than Smule. I have been searching karaoke app and I once discovered an offline karaoke app called Singalong and Sing Karaoke app. You can download the song you like and sing it offline whenever you go and it's all free. You just need more space in your device though. Overall with my experience, you can try Star maker maybe you will like it.